U.S. patent number 4,939,181 [Application Number 07/436,750] was granted by the patent office on 1990-07-03 for polyethylene composition, objects made therefrom and process for the manufacture of foamed objects.
This patent grant is currently assigned to Stamicarbon B.V.. Invention is credited to Franciscus J. J. Haselier.
United States Patent |
4,939,181 |
Haselier |
July 3, 1990 |
Polyethylene composition, objects made therefrom and process for
the manufacture of foamed objects
Abstract
The invention relates to polyethylene compositions comprising
20-98 wt. % branched polyethylene (a) with a density of between 915
and 940 kg/m.sup.3 and a melt flow index of between 0.05 and 40
dg/minute, prepared by a high pressure radical process, and 2-80
wt. % substantially linear polyethylene (b) with a density of
between 850 and 915 kg/m.sup.3, a melt flow index of between 0.05
and 25 dg/minute and a DSC crystallinity at 23.degree. C. of at
least 10%, prepared with the aid of a transition metal catalyst,
the difference between the highest crystallization temperature of
branched polyethylene (a) and the highest DSC crystallization
temperature of linear polyethylene (b) being at most 10.degree. C.
and the mixture having a modulus of elasticity of at most 280
N/mm.sup.2 and objects made therefrom. These polyethylene
compositions, when processed to foamed objects, have a high
resistance to high temperatures as well as a high flexibility.
Inventors: |
Haselier; Franciscus J. J.
(Schinnen, NL) |
Assignee: |
Stamicarbon B.V. (Geleen,
NL)
|
Family
ID: |
19852325 |
Appl.
No.: |
07/436,750 |
Filed: |
November 15, 1989 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
337874 |
Apr 14, 1989 |
|
|
|
|
Foreign Application Priority Data
|
|
|
|
|
May 19, 1988 [NL] |
|
|
8801297 |
|
Current U.S.
Class: |
521/81; 264/54;
521/134; 264/53; 521/79; 521/143 |
Current CPC
Class: |
C08J
9/0061 (20130101); C08L 23/06 (20130101); C08L
23/0815 (20130101); C08L 23/06 (20130101); C08L
2666/06 (20130101); C08L 23/0815 (20130101); C08L
2666/06 (20130101); C08J 2423/00 (20130101); C08J
2323/04 (20130101) |
Current International
Class: |
C08L
23/08 (20060101); C08L 23/00 (20060101); C08L
23/06 (20060101); C08J 9/00 (20060101); C08J
009/10 (); C08J 009/14 () |
Field of
Search: |
;521/81,79,134,143
;264/53,54 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0256724 |
|
Feb 1988 |
|
EP |
|
58-093741 |
|
Jun 1983 |
|
JP |
|
59-149941 |
|
Aug 1984 |
|
JP |
|
61-258849 |
|
Nov 1986 |
|
JP |
|
62-010150 |
|
Jan 1987 |
|
JP |
|
62-064846 |
|
Mar 1987 |
|
JP |
|
58485 |
|
Jul 1969 |
|
LU |
|
692856 |
|
May 1969 |
|
ZA |
|
86/00628 |
|
Jan 1986 |
|
WO |
|
Primary Examiner: Foelak; Morton
Attorney, Agent or Firm: Cushman, Darby and Cushman
Parent Case Text
This is a division of application No. 07/337,874, filed Apr. 14,
1989.
Claims
I claim:
1. Process for the manufacture of foamed objects by mixing a
polyethylene composition with at least one or more foaming agents
at increased pressure and temperature and passing the composition
via an extruder through an extrusion opening into a zone with a
lower pressure and temperature, wherein the polyethylene
composition includes 20-98 wt % branched polyethylene (a) with a
density of between 915 and 940 kg/m.sup.3 and a melt flow index of
between 0.05 and 40 dg/minute, prepared by a high pressure radical
process, and 2-80 wt % substantially linear polyethylene (b) with a
density of between 850 and 915 kg/m.sup.3, a melt flow index of
between 0.05 and 25 dg/minute and a DSC crystallinity at 23.degree.
C. of at least 10%, prepared with the aid of a transition metal
catalyst, the difference between the highest crystallization
temperature of branched polyethylene (a) and the highest DSC
crystallization temperature of linear polyethylene (b) being at
most 10.degree. C. and the mixture having a modulus of elasticity
of at most 280 N/mm.sup.2.
2. Process according to claim 1, characterized in that the foaming
agents are physical foaming agents.
3. Process according to claim 1, characterized in that the
polyethylene composition is in addition mixed with one or more
crosslinking agents.
4. Process according to claim 1, characterized in that the
polyethylene composition is in addition mixed with one or more
lubricants.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a polyethylene composition and objects
made therefrom. The invention also relates to a process for the
manufacture of foamed objects from the polyethylene
composition.
Foamed objects from low density polyethylene (LDPE) can be made by
techniques which have been known for a long time. (Plastic Foams
Part 1, Kurt C. Frisch & James H. Saunders (Eds.), pp 281-292).
Such a polyethylene has a density of between 915 and 940 kg/m.sup.3
and is made in a high pressure process with the aid of one or more
radical initiators. Foamed products from this LDPE have excellent
properties that can be adjusted at will to suit any of a broad
range of applications, for example by making the cells open or
closed as desired, or large or small, in a wide variety of foam
densities and foam shapes.
Thanks to these properties, objects from foamed LDPE are broadly
applicable, e.g. as insulation material. Open-cell foams, for
example, are used for acoustic insulation and closed-cell foams for
thermal insulation. Further, LDPE foams are suitable for
application as packaging for fragile or delicate objects, on
account of their good energy-absorbing properties and their
generally high resistance to chemicals.
The several applications impose different requirements on the foam,
e.g. softness, flexibility, cold brittleness, environmental stress
crack resistance (ESCR) and the like. It is known that these
properties are increasingly present if the foams are made of LDPE
with lower densities and/or with increasing amounts of incorporated
polar comonomers, e.g. vinyl acetate, acrylate, methacrylate,
methyl methacrylate and the like. When such polar copolymers are
used, the above-mentioned properties of LDPE foams can to a greater
extent be adjusted to the requirements than in the case of the
homopolymer LDPE.
However, a disadvantage of polar copolymer foams is that, although
the flexibility increases with the amount of comonomer
incorporated, the high temperature resistance of the foam
decreases. The softening and melting range of polar copolymers lies
at lower temperatures than the softening and melting range of LDPE
homopolymer. This limits the field of application of flexible
foams. Further, the polar copolymers are more likely to give rise
to sticking problems during their conversion to (foamed)
objects.
The object of the invention is to obtain polyethylene compositions
which, when processed to foamed objects, have a high resistance to
high temperatures as well as a high flexibility.
This object is achieved by a polyethylene composition comprising
20-98 wt% branched polyethylene (a) with a density of between 915
and 940 kg/m.sup.3 and a melt flow index of between 0.05 and 40
dg/minute, prepared by a high-pressure radical process, and 2-80
wt% of a substantially linear polyethylene (b) with a density of
between 850 and 915 kg/m.sup.3, a melt flow index of between 0.05
and 25 dg/minute and a DSC crystallinity at 23.degree. C. of at
least 10%, made with the aid of a transition metal catalyst, the
difference between the highest DSC crystallization temperature of
branched polyethylene (a) and the highest DSC crystallization
temperature of linear polyethylene (b) being at most 10.degree. C.
and the mixture having a modulus of elasticity of at most 280
N/mm.sup.2.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the DSC crystallization curves of the compositions of
Example I;
FIG. 2 shows the DSC crystallization curves of the compositions of
Example II;
FIG. 3 shows the DSC crystallization curves of the compositions of
Example III;
FIG. 4 shows the DSC crystallization curves of the compositions of
Example IV;
FIG. 5 shows the DSC crystallization curves of the compositions of
Example V;
FIG. 6 shows the DSC crystallization curves of the compositions of
Example VI;
FIG. 7 shows the DSC crystallization curves of the compositions of
Example VII;
FIG. 8 shows the DSC crystallization curves of the compositions of
Example VIII;
FIG. 9 shows the DSC crystallization curves of the compositions of
Example IX;
FIG. 10 shows the DSC crystallization curves of the compositions of
Example X;
FIG. 11 shows the DSC crystallization curves of the compositions of
Comparative example 1;
FIG. 12 shows the DSC crystallization curves of the compositions of
Comparative example 2;
FIG. 13 shows the DSC crystallization curves of the compositions of
Comparative example 3;
FIG. 14 shows the DSC crystallization curves of the compositions of
Comparative example 4;
FIG. 15 shows the DSC crystallization curves of the compositions of
Comparative example 5;
FIG. 16 shows the DSC crystallization curves of the compositions of
Comparative example 6.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that LDPE foams with favourable properties can be
made when a high melt drawing force as well as a high maximum melt
draw ratio are present in the molten material. In this way, it is
prevented that the foam collapses during the transition from molten
foam to crystallized foam in foaming processes with physical
foaming agents, or during expansion in foaming processes with
chemical foaming agents. To this end, the melt drawing force should
be at least 10 cN and preferably at least 15 cN, while the maximum
melt draw ratio should be at least 30 and preferably 40.
The E-modulus (modulus of elasticity), which is a measure of the
rigidity of the unfoamed starting material, is in LDPE homopolymer
often higher than would be desirable for a good flexibility when
the material is processed to a (foamed) object. For a good
flexibility, the E-modulus should be at most 280 N/mm.sup.2, and
preferably at most 250 N/mm.sup.2, in particular at most 230
N/mm.sup.2. At an LDPE density of 915 kg/m.sup.3, the E-modulus is
about 160 N/mm.sup.2, and it increases with increasing density.
However, the high-temperature resistance of a foamed object from
such material is too low for many applications (less than
100.degree. C.). A foamed object from an LDPE with a density of 925
kg/m.sup.3 is resistant to temperatures of more than 100.degree.
C., but this LDPE has an E-modulus of about 350 N/mm.sup.2.
Surprisingly, it has been found that polyethylene compositions
according to the invention have a melt drawing force of at least 10
cN, in particular at least 15 cN, and a melt draw ratio of at least
30, in particular at least 40, and that, when they are processed to
foamed objects, they yield soft and flexible foams that have a good
high-temperature resistance (more than 100.degree. C.). From
GB-A-1,552,435 and EP-A-0016348, mixtures of branched polyethylene
with a density of between 915 and 935 kg/m.sup.3 and a linear
polyethylene with a density of between 918 and 940 kg/m.sup.3 are
known. These have the favourable properties of the known LDPE, but
they, too, lack flexibility and softness.
The polyethylene (a) of compositions according to the invention is
preferably polyethylene homopolymer (LDPE) with a density of
between 918 and 928 kg/m.sup.3, in particular between 922 and 928
kg/m.sup.3 ; the melt flow index is preferably between 0.1 and 30
dg/minute, in particular below 10 dg/minute. It is produced in the
usual manner, in a high pressure process with the aid of one or
more radical initiators. This process yields a polyethylene that
has long side chains and that is therefore sometimes called a
branched polyethylene.
Polyethylene (a) according to the invention may also be a copolymer
of ethylene with vinyl acetate, acrylic acid and the like, with a
percentage of incorporated polar comonomer of at most 2 mole %, or
a mixture of LDPE with a polar copolymer (with a copolymer
incorporation percentage that may in this case also be higher than
2 mole %, e.g. 8 mole % or more). In these cases, an LDPE
homopolymer weight percentage of 50 is recommendable.
The polyethylene (b) of the compositions according to the invention
is a linear polyethylene with a density of, preferably, between 880
and 912 kg/m.sup.3, in particular less than 910 kg/m.sup.3, and a
melt flow index preferably between 0.1 and 20 dg/minute, in
particular below 15 dg/minute. It is a copolymer of ethylene and
one or more 1-alkenes with 3 to 18 carbon atoms in an amount of 10
to 50 wt %, referred to the ethylene, and possibly a small amount
of dienes. Copolymers with 4 to 12 carbon atoms, in particular
1-butene, 1-hexene, 4-methylpentene-1 and 1-octene, are preferred.
It has mainly short side chains and considerably fewer long side
chains than LDPE, which is why it is also called linear
polyethylene. It has a crystallinity of more than 10% at 23.degree.
C., as determined by the Differential Scanning Calorimetry method,
and preferably more than 15%, in particular more than 20%. It is
produced with the aid of transition metal catalysts, preferably the
so-called Ziegler-Natta catalysts, in particular those catalysts
comprising at least a titanium compound and an aluminum compound, a
magnesium compound and/or a vanadium compound and/or a chloride
possibly also being present. The process is known as such and can
take place at high or low pressures and at high or low
temperatures. Particular preference is given to a process in the
presence of a dispersing agent, with the pressure not exceeding 200
bar, in particular not exceeding 100 bar, and the temperature being
higher than 110.degree. C., in particular higher than 135.degree.
C.
The amounts of the polyethylene components (a) and (b) slightly
depends on the application. In general, an amount of 30-90 wt % of
polyethylene (a) and 10-70 wt % of polyethylene (b) is to be
preferred, in particular 40-85 wt % of polyethylene (a) and 15-60
wt % of polyethylene (b), more in particular 50-85 wt % of
polyethylene (a) and 15-50 wt % of polyethylene (b).
The mixing can be done in a usual manner, for example by tumbling
of granular polyethylene, by using a Henschel mixer for powdered
polyethylene or in a Banbury mixer or an extrusion mixer. The
polyethylenes (a) and (b) can also very well be fed directly, in
the appropriate ratio, to the extrusion device that is generally
used to convert polyethylene to objects, without prior mixing. The
manner of mixing, within the usual time and temperature ranges, is
not critical to the invention.
Polyethylene compositions according to the invention can be
converted in many processes known as such, e.g. injection moulding,
rotational moulding, blow moulding, profile extrusion, film
manufacturing, etc. However, the polyethylene compositions are
particularly suitable for conversion to foamed objects. This can be
done in different manners, which are generally divided into
processes with chemical foaming agents and processes with physical
foaming agents.
In chemical foaming, a substance is added to the polyethylene
mixture as foaming agent which, under certain conditions (e.g. a
temperature rise), which are well-known to a person skilled in the
art, decomposes into gaseous components with generation of
pressure, thus causing the polyethylene to foam.
In physical foaming, the polyethylene composition is at an
increased pressure and temperature mixed, usually in an extrusion
device, with one or more foaming agents that are gaseous at normal
pressure and room temperature, and is then exposed to a lower
pressure and temperature, as a result of which the mixture expands
and the polyethylene starts to foam. In this process, the
polyethylene also cools down and crystallizes. In physical foaming,
usually use is made of (mixtures of) halogenated hydrocarbons,
(mixtures of) gaseous alkanes or mixtures of these substances.
Commonly used amounts are e.g. 0.01-0.6 gram molecule of foaming
agent per 100 parts polyethylene. In this way, foam densities are
obtained which can vary between 5 and 400 kg/m.sup.3, depending on
the conditions applied (type of foaming agent, type of seeding
agent, temperature, pressure, additives, etcetera). A person
skilled in the art well knows how to vary these conditions
according to the requirements.
In foam production, whether or not a good foam quality is obtained
depends to an important extent on the crystallization behavior of
the polyethylene. The crystallization behaviour of polymers can be
determined by the Differential Scanning Calorimetry (DSC) method.
The crystallization curves determined with this method show one or
more peaks, depending on the molecular structure of the materials
tested. The tops of these peaks are called the crystallization
temperatures. It has been found that the difference between the
highest DSC crystallization temperature of branched polyethylene
(a) and the highest crystallization temperature of linear
polyethylene (b) may be at most 10.degree. C., since otherwise the
mixture formed crystallizes across too broad a crystallization
range, resulting in undesirable demixing. A difference of at most
8.degree. C. is to be preferred, in particular a difference of at
most 7.degree. C. The DSC crystallization curves of the
compositions according to the invention preferably have at most one
peak between 125.degree. C. and 95.degree. C., which peak may have
a shoulder or may be broad (more than about 10.degree. C. at the
base) or narrow (less than about 10.degree. C. at the base). Peaks
without shoulders are to be preferred, in particular narrow
peaks.
Polyethylene compositions according to the invention are
excellently suitable for manufacturing foamed objects. It is
recommendable to use physical foaming agents, such as pentane,
chlorofluorohydrocarbons, carbon dioxide, nitrogen, mixtures
thereof, etc. The use of chemical foaming agents, such as
azodicarbonamide or azodiformamide and the like is also
possible.
The high-temperature resistance of polyethylene compositions
according to the invention can be considerably increased if a
crosslinking agent is used, e.g. organic peroxides, oxygen,
multifunctional allyl- and/or vinyl monomers, and azido- and
vinyl-functional silanes. Crosslinking can take place to a greater
or lesser extent, as desired, which can be achieved by varying the
amount of crosslinking agent, e.g. between 0.005 and 5.0 wt %
referred to the total composition. In doing so, the good
flexibility is retained.
The polyethylene compositions can in addition comprise other
substances, such as seeding agents, foam stabilizers, thermal
stabilizers, UV-stabilizers, antistatic agents, lubricants,
antioxidants, antiblocking agents, fillers, pigments, processing
aids, etc.
For the above-described physical foaming technique, the presence of
a lubricant, e.g. 0.05-1.5 wt % oleamide, is desirable. In chemical
foam processing, often also the presence of a so-called kicker is
desired, which ensures synchronization of the decompositions of
crosslinking agent and foaming agent. In general, this is a metal
oxide, in particular zinc oxide.
Foamed objects according to the invention can be manufactured in
any desired shape, such as profiles (e.g. rods and tubes),
granules, films, layers on films of other materials, etc. It is
also possible to make foamed objects according to the invention by
causing foamed granules to stick or melt together by heating. This
technique is known as such.
The invention will now be elucidated with reference to a few
examples, without, however, being limited thereto.
Various polyethylene mixtures were composed as indicated in the
examples.
All copolymers were octene-1 copolymers and had a DSC crystallinity
at 23.degree. C. of more than 10%.
In FIG. 1, the DSC crystallization curves of the compositions of
Example I are shown, in FIG. 2 those of Ex. II, in FIG. 3 those of
Ex. III, in FIG. 4 those of Ex. IV, in FIG. 5 those of Ex. V, in
FIG. 6 those of Ex. VI, in FIG. 7 those of Ex. VII, in FIG. 8 those
of Ex. VIII, in FIG. 9 those of Ex. IX, in FIG. 10 those of Ex. X,
in FIG. 11 those of Comparative Example 1, in FIG. 12 those of
Comp. Ex. 2, in FIG. 13 those of Comp. Ex. 3, in FIG. 14 those of
Comp. Ex. 4, in FIG. 15 those of Comp. Ex. 5, and in FIG. 16 those
of Comp. Ex. 6.
The density (d) was measured according to ISO 1183 (D), the melt
flow index (MFI) according to ISO 1133 (A/4).
The melt drawing force (MDF) and the maximum melt draw ratio (MDR)
were determined by extruding an amount of the polyethylene through
a die with a height of 8.0 mm and a diameter of 2.0 mm, at a
temperature of 130.degree. C. and with a yield of 0.25 g/minute,
and drawing the extrudate to a thread until the thread broke. The
force required for drawing and the draw ratio at break are the melt
drawing force (in Newtons) and the maximum melt draw ratio,
respectively.
The E-modulus was determined according to DIN 53457
(N/mm.sup.2).
For the DSC measurements, use was made of a measuring set-up
comprising a Perkin-Elmer DSC-2, arranged on-line with a Tektronix
4052 computer, a Hewlett-Packard 3495 A scanner-multiplexer and an
HP 3455A digital Volt meter (51/2--51/2 digit).
The measurements were performed according to the `continuous`
measuring procedure of V. B. F. Mathot et al., J. Thermal Anal.
Vol. 28, 349-358 (1983), reproduced on a relative scale.
The measurements were performed under nitrogen; after heating to
180.degree. C. and a waiting time of 5 minutes, the sample was
cooled to 45.degree. C. at a scan rate of 5.degree. C./minute. The
samples weighed 5 mg and were weighed to the nearest 1 microgram
with a Mettler Me 22/36 electronic microbalance. Every 0.2.degree.
C., the temperature and the measuring result corresponding to that
temperature were recorded.
The crystallization temperatures mentioned in the tables were
determined by this DSC method.
EXAMPLE I
______________________________________ Polyethylene a: d = 923.5
kg/m.sup.3 ; MFI = 0.8 dg/minute. Polyethylene b: d = 911
kg/m.sup.3 ; MFI = 2.5 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 34 38 254 98.5 narrow
75/25 28 55 227 103 broad 0/100 4 >757 177 107.5 narrow
______________________________________
EXAMPLE II
______________________________________ Polyethylene a: d = 923.5
kg/m.sup.3 ; MFI = 0.8 dg/minute. Polyethylene b: d = 906
kg/m.sup.3 ; MFI = 2.5 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 34 38 254 98.5 narrow
75/25 29 53 221 102 narrow 0/100 2 >757 133 105.5 narrow
______________________________________
EXAMPLE III
______________________________________ Polyethylene a: d = 923.5
kg/m.sup.3 ; MFI = 0.8 dg/minute. Polyethylene b: d = 902
kg/m.sup.3 ; MFI = 2.9 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 34 38 254 98.5 narrow
75/25 27 54 215 102 narrow 0/100 2 >757 110 105.5 narrow
______________________________________
EXAMPLE IV
______________________________________ Polyethylene a: d = 926
kg/m.sup.3 ; MFI = 2.0 dg/minute. Polyethylene b: d = 911
kg/m.sup.3 ; MFI = 2.5 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 36 65 302 101 narrow
75/25 28 86 264 103.5 broad 0/100 4 >757 177 107.5 narrow
______________________________________
EXAMPLE V
______________________________________ Polyethylene a: d = 926
kg/m.sup.3 ; MFI = 2.0 dg/minute. Polyethylene b: d = 902
kg/m.sup.3 ; MFI = 2.9 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 36 65 302 101 narrow
85/15 22.5 67 259 101.5 narrow 75/25 21.5 98 242 102.5 narrow 0/100
2 >757 110 105.5 narrow
______________________________________
EXAMPLE VI
______________________________________ Polyethylene a: d = 926
kg/m.sup.3 ; MFI = 1.6 dg/minute. Polyethylene b: d = 902
kg/m.sup.3 ; MFI = 2.9 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 28 78 295 100 narrow
75/25 22 105 243 102 narrow 0/100 2 >757 110 105.5 narrow
______________________________________
EXAMPLE VII
______________________________________ Polyethylene a: d = 926
kg/m.sup.3 ; MFI = 1.4 dg/minute. Polyethylene b: d = 902
kg/m.sup.3 ; MFI = 2.9 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 38 72 304 100 narrow
75/25 23 97 248 102 narrow 0/100 2 >757 110 105.5 narrow
______________________________________
EXAMPLE VIII
______________________________________ Polyethylene a: d = 926
kg/m.sup.3 ; MFI = 0.3 dg/minute. Polyethylene b: d = 902
kg/m.sup.3 ; MFI = 2.9 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 25 29 308 100 narrow
75/25 25 101 245 102 narrow 0/100 2 >757 110 105.5 narrow
______________________________________
EXAMPLE IX
______________________________________ Polyethylene a: d = 927
kg/m.sup.3 ; MFI = 1.3 dg/minute. Polyethylene b: d = 902
kg/m.sup.3 ; MFI = 2.9 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 21 40 320 102 narrow
75/25 22? 90 269 104 narrow 70/30 27.4 71 263 104.5 narrow 0/100 2
>757 110 105.5 narrow ______________________________________
EXAMPLE X
______________________________________ Polyethylene a: d = 927
kg/m.sup.3 ; MFI = 1.5 dg/minute. Polyethylene b: d = 902
kg/m.sup.3 ; MFI = 2.9 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 17.9 64 323 101.5
narrow 75/25 20.5 110 263 103 broad 70/30 23.1 100 253 103.5 broad
0/100 2 >757 110 105.5 narrow
______________________________________
COMPARATIVE EXAMPLE 1
______________________________________ Polyethylene a: d = 920
kg/m.sup.3 ; MFI = 1.9 dg/minute. Polyethylene b: d = 921
kg/m.sup.3 ; MFI = 4.1 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 29 43 195 95 narrow
75/25 26 66 228 97, 105 -- 0/100 5 >757 318 107.5 narrow
______________________________________
COMPARATIVE EXAMPLE 2
______________________________________ Polyethylene a: d = 920
kg/m.sup.3 ; MFI = 1.9 dg/minute. Polyethylene b: d = 911
kg/m.sup.3 ; MFI = 5.5 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 29 43 195 95 narrow
85/15 24 58 193 96.5, 103 shoulder 75/25 22 76 190 96, 105 -- 50/50
17.5 147 186 95, 107 -- 0/100 4 >757 177 108 narrow
______________________________________
COMPARATIVE EXAMPLE 3
______________________________________ Polyethylene a: d = 920
kg/m.sup.3 ; MFI = 1.9 dg/minute. Polyethylene b: d = 919
kg/m.sup.3 ; MFI = 4.6 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 29 43 195 95 narrow
75/25 25 80 215 95, 105 -- 0/100 4 >757 283 107.5 narrow
______________________________________
COMPARATIVE EXAMPLE 4
______________________________________ Polyethylene a: d = 922
kg/m.sup.3 ; MFI = 0.8 dg/minute. Polyethylene b: d = 911
kg/m.sup.3 ; MFI = 5.5 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 31 30 236 97 narrow
90/10 24.5 35 218 98 broad 85/15 27 28 215 99 broad 75/25 26 45 211
97.5, 104.5 -- 0/100 5 >757 177 108 narrow
______________________________________
COMPARATIVE EXAMPLE 5
______________________________________ Polyethylene a: d = 931
kg/m.sup.3 ; MFI = 1.7 dg/minute. Polyethylene b: d = 921
kg/m.sup.3 ; MFI = 5.5 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 39 85 428 104.5 narrow
85/15 20 82 402 107 narrow 75/25 17 97 392 107 narrow 50/50 14 198
361 108 narrow 0/100 5 >757 318 107.5 narrow
______________________________________
COMPARATIVE EXAMPLE 6
______________________________________ Polyethylene a: d = 931
kg/m.sup.3 ; MFI = 1.7 dg/minute. Polyethylene b: d = 911
kg/m.sup.3 ; MFI = 5.5 dg/minute. MDF MDR E-mod. DSC cryst. a/b cN
x N/mm.sup.2 temp., .degree.C. peak
______________________________________ 100/0 39 85 428 104.5 narrow
75/25 17 135 346 106.5 narrow 0/100 4 >757 177 108 narrow
______________________________________
EXAMPLE XI
Of a number of polyethylene compositions from the examples, round
foam profiles were made with the aid of an extruder commonly used
for foam extrusion. The temperature of the extruder head was set to
3 (.OMEGA. 0.5).degree. C. above the (highest) crystallization
temperature of the polyethylene composition.
As blowing agent, a 50/50 (m/m) mixture of Freon 12
(dichlorotetrafluoroethane) and Freon 114 (dichlorofluoromethane)
was added, in an amount of 15 parts by weight of blowing agent and
85 parts by weight of polymer. 0.2% seeding agent was added to the
polymer in the form of a masterbatch (LDPE with 20 wt % sodium
bicarbonate and citric acid), and lubricant was also added (0.2 wt
% oleamide).
The round foam profile thus formed was assessed in terms of
flexibility and softness by manual bending and compression,
respectively.
The high-temperature resistance was determined by keeping the round
foam profile at 100.degree. C. for 6 weeks. If the profile was
sticky after 6 weeks, it was rated -, and if it was not sticky it
was rated +.
The results are listed in the following table.
__________________________________________________________________________
foam foam density % closed high temp. Example processing kg/m.sup.3
cells flexibility softness resistance
__________________________________________________________________________
IV 100/o V 100/o good 36 82 - - + VI 100/o good 37 83 - - + 1 100/o
2 100/o good 36 77 + + - 3 100/o 5 100/o 6 100/o good 38 84 -- -- +
III o/100 V o/100 VI o/100 VII o/100 collapse VIII o/100 IX o/100 X
o/100 1 o/100 collapse 5 o/100 2 o/100 2 o/100 collapse 6 o/100 VI
75/25 good 38 78 ++ ++ + VII 75/25 good 34 80 ++++ ++++ + IX 70/30
good 36 72 +++ ++++ + X 70/30 good 34 79 ++ ++ + 1 75/25 collapse 4
75/25 collapse 6 75/25 good 35 74 - - +
__________________________________________________________________________
* * * * *